What is the minimum age of concrete cylinders before testing to ensure reliable results?

The minimum age of concrete cylinders before testing is typically set at 28 days to ensure reliable results due to the hydration process of concrete. This 28-day period allows the concrete to reach its intended compressive strength, as concrete continues to cure and gain strength over time. The majority of standard testing procedures, including those set by ACI (American Concrete Institute), reference this timeframe because it represents a point where the concrete has undergone substantial curing and strength development.

Testing at this age provides a more accurate reflection of the concrete's strength characteristics, allowing for consistent and reliable results that are critical in assessing the quality and performance of the concrete used in construction. It's also worth noting that while concrete can continue to improve strength beyond 28 days, this timeframe is well-established as a standard for initial strength evaluation.